The present disclosure relates to an electrosurgical instrument for performing endoscopic surgical procedures. More particularly, the present disclosure relates to a endoscopic bipolar electrosurgical forceps which utilizes linear displacement of an insulating yoke to grasp and seal tissue between two opposing jaw members.
A hemostat or forceps is a simple plier-like tool which uses mechanical action between its jaws to constrict vessels and is commonly used in open surgical procedures to grasp, dissect and/or clamp tissue. Electrosurgical forceps are similar clamping devices which utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to cause coagulation and/or cauterization.
Over the last several decades, more and more surgeons are abandoning traditional open methods of gaining access to vital organs and body cavities in favor of endoscopes and endoscopic instruments which access organs through small puncture-like incisions. Endoscopic instruments are inserted into the patient through a cannula, or port, that has been made with a trocar. Typical sizes for cannulas range from three millimeters to twelve millimeters. Smaller cannulas are usually preferred, and this presents a design challenge to instrument manufacturers who must find ways to make surgical instruments that fit through the cannulas.
Certain surgical procedures require cutting blood vessels or vascular tissue. However, due to space limitations surgeons can have difficulty suturing vessels or performing other traditional methods of controlling bleeding, e.g., clamping and/or tying-off transected blood vessels. Very small blood vessels, in the range below two millimeters in diameter, can often be closed using standard electrosurgical techniques. If a larger vessel is severed, it may be necessary for the surgeon to convert the endoscopic procedure into an open-surgical procedure and thereby abandon the benefits of laparoscopy.
Several journal articles have disclosed methods for sealing small blood vessels using electrosurgery. An article entitled Studies on Coagulation and the Development of an Automatic Computerized Bipolar Coagulator, J. Neurosurg., Volume 75, July 1991, describes a bipolar coagulator which is used to seal small blood vessels. The article states that it is not possible to safely coagulate arteries with a diameter larger than 2 to 2.5 mm. A second article is entitled Automatically Controlled Bipolar Electrocoagulationxe2x80x94xe2x80x9cCOA-COMPxe2x80x9d, Neurosurg. Rev. (1984), pp. 187-190, describes a method for terminating electrosurgical power to the vessel so that charring of the vessel walls can be avoided.
By utilizing an electrosurgical forceps, a surgeon can either cauterize, coagulate/desiccate and/or cut tissue and/or simply reduce or slow bleeding, by controlling the intensity, frequency and duration of the electrosurgical energy applied to the tissue. Generally, the electrical configuration of electrosurgical forceps can be categorized in two classifications: 1) monopolar electrosurgical forceps; and 2) bipolar electrosurgical forceps.
Monopolar forceps utilize one active electrode associated with the clamping end effector and a remote patient return electrode or pad which is typically attached externally to the patient. When the electrosurgical energy is applied, the energy travels from the active electrode, to the surgical site, through the patient and to the return electrode.
Bipolar electrosurgical forceps utilize two generally opposing electrodes which are disposed on the inner opposing surfaces of the end effectors and which are both electrically coupled to an electrosurgical generator. Each electrode is charged to a different electric potential. Since tissue is a conductor of electrical energy, when the effectors are utilized to grasp tissue therebetween, the electrical energy can be selectively transferred through the tissue.
Several bipolar endoscopic instruments are known. For example: U.S. Pat. No. 3,938,527 discloses a bipolar endoscopic instrument for tubal cauterization; U.S. Pat. No. 5,250,047 discloses a bipolar endoscopic instrument with a replaceable electrode tip assembly; U.S. Pat. No. 5,445,638 discloses a bipolar coagulation and cutting forceps with first and second conductors extending from the distal end; U.S. Pat. No. 5,391,166 discloses a bipolar endoscopic instrument having a detachable working end; and U.S. Pat. No. 5,342,359 discloses a bipolar coagulation device.
In order to effect a proper seal with larger vessels, two predominant mechanical parameters must be accurately controlledxe2x80x94the pressure applied to the vessel and the gap between the electrodes both of which affect thickness of the sealed vessel. More particularly, accurate application of the pressure is important to oppose the walls of the vessel, to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue, to overcome the forces of expansion during tissue heating and to contribute to the end tissue thickness which is an indication of a good seal. In some instances a fused vessel wall is optimum between 0.001 and 0.006 inches. Below this range, the seal may shred or tear and above this range the lumens may not be properly or effectively sealed.
Electrosurgical methods may be able to seal larger vessels using an appropriate electrosurgical power curve, coupled with an instrument capable of applying a large closure force to the vessel walls. It is thought that the process of coagulating small vessels is fundamentally different than electrosurgical vessel sealing. For the purposes herein, coagulation is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried and vessel sealing is defined as the process of liquefying the collagen in the tissue so that it crosslinks and reforms into a fused mass. Thus, coagulation of small vessels is sufficient to permanently close them. Larger vessels need to be sealed to assure permanent closure.
Numerous bipolar electrosurgical forceps have been proposed in the past for various open surgical procedures. However, some of these designs may not provide uniformly reproducible pressure to the blood vessel and may result in an ineffective or non-uniform seal. For example, U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. No. 4,005,714 to Hiltebrandt, U.S. Pat. Nos. 4,370,980, 4,552,143, 5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern et al., U.S. Pat. No. 5,484,436 to Eggers et al., all relate to electrosurgical instruments for coagulating, cutting and/or sealing vessels or tissue.
These instruments rely on clamping pressure alone to procure proper sealing thickness and are not designed to take into account gap tolerances and/or parallelism and flatness requirements which are parameters which, if properly controlled, can assure a consistent and effective tissue seal. For example, it is known that it is difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure alone for either of two reasons: 1) if too much force is applied, there is a possibility that the two poles will touch and energy will not be transferred through the tissue resulting in an ineffective seal; or 2) if too low a force is applied, a thicker less reliable seal is created.
As mentioned above, in order to properly and effectively seal larger vessels, a greater closure force between opposing jaw members is required. It is known that a large closure force between the jaws typically requires a large moment about the pivot for each jaw. This presents a challenge because the jaw members are typically affixed with pins which are positioned to have a small moment arms with respect to the pivot of each jaw member. A large force, coupled with a small moment arm, is undesirable because the large forces may shear the pins. It is also undesirable to increase the moment arm of the pins because the physical size of the jaw members and other component parts might not fit through a cannula.
Thus, a need exists to develop a bipolar forceps which effectively seals vascular tissue and solves the problem of providing a large closure force between the opposing jaws members using a compact design that is capable of fitting through a cannula without risking structural failure of the instrument yoke.
The present disclosure relates to a endoscopic bipolar forceps for clamping and sealing tissue which includes first and second jaw members pivotally attached in opposing relation relative to one another which are movable from a first open position wherein the jaw members are disposed in spaced relation relative to one another to a second clamping position wherein the jaw members cooperate to grasp tissue therebetween. A drive rod assembly connects each of the jaw members to a source of electrical energy such that the jaw members are capable of conducting bipolar energy through the tissue held therebetween. A handle is attached to the drive rod assembly and imparts movement of the first and second jaw members from the first and second positions. At least one stop member preferably made from an insulating material is attached to the jaw members for controlling the distance between the jaw members.
Preferably, the handle includes an actuator having a lost motion connection between the jaw members and the actuator for transferring user manipulation of the actuator to the jaw members so as to maintain a predetermined or maximum clamping force within a preferred range irrespective of the user manipulation during sealing of the tissue between the jaw members.
In one embodiment, the forceps includes a rotating assembly for controlling the rotational movement of the jaw members. In another embodiment, the jaw members and the drive assembly are connected by a cam follower mechanical linkage for imparting movement of the jaw members relative to one another.
Another embodiment of the present disclosure includes a bipolar forceps having first and second jaw members pivotally attached in opposing relation relative to one another, the jaw members being movable from a first open position wherein the jaw members are disposed in spaced relation relative to one another to a second clamping position wherein the jaw members cooperate to grasp tissue therebetween. A drive rod assembly connects each of the jaw members to a source of electrical energy such that the jaw members are capable of conducting bipolar energy through the tissue held therebetween. A yoke member is attached to the distal end of the drive rod assembly and between the jaw members. Preferably, a handle is attached to the drive rod assembly and imparts linear movement to the yoke member which, in turn, imparts movement of the two opposing jaw members relative to one another by virtue of a cam-follower mechanical linkage.
Preferably, each jaw member includes a flange which extends therefrom and the yoke includes a pair of shoulder portions which are dimensioned to abut the flanges when the jaw members are moved into the second position. The shoulder portions relieve shear stresses on the cam-follower linkage during clamping and sealing of the tissue.
In another embodiment, each of the jaw members includes a cam slot located therethrough and the yoke includes at least one corresponding detent which engages the cam slots such that movement of the yoke imparts movement of the jaw members relative to one another. Preferably, each of the cam slots includes a cul-de-sac positioned therein to relieve shear stress on the detent approximately when the shoulder portions of the yoke member engage the flanges of the jaw members. Preferably, the inner periphery of the cam slots are shaped to impart at least two different movements to the jaw members relative to one another.